Design and Simulation of a Novel Single-Chip Integrated MEMS Accelerometer Gyroscope

Round 1

Reviewer 1 Report

The presentation of figure 6 could be improved. There is a correction to make on line 218. The results could be described with more details.

Author Response

The presentation of figure 6 could be improved. There is a correction to make on line 218. The results could be described with more details.

(1) Revised the presentation of Figure 6 (Figure 7 in the revised manuscript).

(2) Corrected description on line 218 (Line 231 in the revised manuscript)..

The simulation results demonstrate that the working frequencies of the DETFs are susceptible to temperature and the resonant frequencies drift reaches 20.1 Hz/ ℃.

(3) Added more details of the results in the conclusion.

Author Response File: Author Response.docx

Reviewer 2 Report

See the attached PDF file. Thank You. 

Comments for author File: Comments.pdf

Author Response

The Authors presents the design and simulation of a single-chip integrated MEMS accelerometer gyroscope by integrating Coriolis vibratory ring gyroscope and differential resonant accelerometer into one single chip structure, measuring both the acceleration and the angular velocity. The paper is well organized and well written and the proposed device is interesting. Moreover, each section is adequately discussed and presented. However, I suggest the authors to address the following points:

1. I suggest the Authors to revise the whole document in order to check the typos.

Thoroughly checked and revised the manuscript.

2. Before the conclusion section, I suggest the Authors to add a comparison table in order to compare this work with other ones present in the literature.

Currently, single-chip integrated MEMS IMUs have low precision and are mainly used in consumer and industrial fields. The high-precision MEMS IMU mainly adopts three single-axis accelerometers and three single-axis gyroscopes through three-dimensional assembly, but there are problems such as large size, high cost, and installation errors.

The single-chip gyroscope accelerometer proposed in this paper integrates the ring gyroscope and resonant accelerometer with high precision performance. When applied to MEMS IMU, the number of devices can be reduced from the traditional 6 to 3, which will have significant advantages in terms of volume and so on.

Since the single-chip integrated gyroscope accelerometer proposed in this paper is an inertial device. Assembling into a MEMS IMU requires the three described devices and corresponding circuit arrangements. Therefore, a systematic comparison of the gyroscope accelerometer presented in this article with a MEMS IMU cannot be reasonably made at present.

Author Response File: Author Response.docx

Reviewer 3 Report

1.       I appreciate the authors proposing an interesting device design for an accelerometer and gyroscope in a single chip. However, in MEMS and microsensors research, the premise is generally accepted if it is validated with experimental results. The major drawback of the present work is that no effort is taken to fabricate the device. The authors should at least comment on the fabrication feasibility of the proposed idea. They should provide a flow diagram with cross-sectional views of each fabrication step and materials and unit process steps.  

2.       Pls, comment on whether any researcher has attempted fabricating the inertial measurement unit (Accelerometer + gyroscope) in a single chip. What are the merits and limitations of such hitherto reported devices? The introduction section needs to be modified with the details on hitherto reported single-chip IMUs with accelerometer and gyroscope.

3.       "Both inertial measurement unit (IMU) and inertial microsystem (IMU) are designed to improve….. "– The same acronym of IMU is used for different devices. I think the second one should be IMS. Pls, comment on how IMS is different from IMU. Rephrasing would improve the clarity, I suppose.

4.       "However, the high precision inertial measurement unit based on MEMS is usually composed of multiple devices, which still has large volume and high power consumption problems." – Pls provide suitable references here. The hybrid assembly of stand-alone accelerometers and gyroscopes to realize an IMU is error-prone for various reasons. Briefly comment on the same.

5.       The manuscript will benefit from thorough proofreading. For example, Line 77 should be "G. H. Bryan" and Line 79, whether the Bryan effect or Brian effect. Pls, check.

6.       Please comment on the rationale for choosing the IMU's geometrical dimensions listed in Table 1.

7.       Even though it is simulation work, authors are suggested to compare the metrics of the proposed IMU with reported accelerometers and gyroscopes. What are the sensitivity, resolution, and other parameters of the gyroscope? Authors have focussed only on the accelerometer's scale factor (i.e., sensitivity) with some temperature studies. Other quantitative metrics of the accelerometer are ignored in the present work—Pls comment.

 

Most of the references are not published in the recent past. The authors may consider updating the references with recent manuscripts on accelerometers and gyroscopes. Also, please ensure that all the references are relevant to the text against which they are mentioned.

Author Response

1. I appreciate the authors proposing an interesting device design for an accelerometer and gyroscope in a single chip. However, in MEMS and microsensors research, the premise is generally accepted if it is validated with experimental results. The major drawback of the present work is that no effort is taken to fabricate the device. The authors should at least comment on the fabrication feasibility of the proposed idea. They should provide a flow diagram with cross-sectional views of each fabrication step and materials and unit process steps.

The processing technology is  the deep dry silicon on glass (DDSOG) process, which is a very commonly used MEMS device fabrication process.

Figure 4: Added the procedures and advantages of the DDSOG process.

In addition, due to the lack of perfect processing conditions in the institutions where the authors work, the processing of the devices is normally carried out by external agencies, resulting in a long processing cycle. After the preparation is completed, we will further publish the relevant test results.

2. Pls, comment on whether any researcher has attempted fabricating the inertial measurement unit (Accelerometer + gyroscope) in a single chip. What are the merits and limitations of such hitherto reported devices? The introduction section needs to be modified with the details on hitherto reported single-chip IMUs with accelerometer and gyroscope.

Currently, single-chip integrated MEMS IMUs have low precision and are mainly used in consumer and industrial fields. The high-precision MEMS IMU mainly adopts three single-axis accelerometers and three single-axis gyroscopes through three-dimensional assembly, but there are problems such as large size, high cost, and installation errors.

At present, MEMS gyroscopes and accelerometers are mainly based on two-dimensional structures, and the realization of single-chip integrated high-precision MEMS IMUs is still relatively difficult. On the one hand, the method of sharing proof mass has the problem of cross-coupling error, and it is difficult to achieve high precision; on the other hand, without sharing proof mass, the measurement of 3-axis angular velocity and 3-axis acceleration on a two-dimensional structure is not yet available in the current working principle of various types of MEMS gyroscopes and accelerometers. Therefore, on the one hand, the research of inertial devices with new working principles is required, and on the other hand, further development of processing technology is required to be compatible with the preparation of devices in more structural forms.

3. "Both inertial measurement unit (IMU) and inertial microsystem (IMU) are designed to improve….. "– The same acronym of IMU is used for different devices. I think the second one should be IMS. Pls, comment on how IMS is different from IMU. Rephrasing would improve the clarity, I suppose.

Introduction: Revised descriptions and acronyms of micro inertial measurement unit and micro inertial navigation system.

IMU (Inertial Measurement Unit) is mainly composed of inertial devices (gyroscope, accelerometer), and outputs the most primitive data, such as acceleration, angular velocity and so on.

INS (Inertial Navigation System) can be understood as a combination of IMU and algorithms, adding algorithms to the original data of the inertial device to output information such as position and carrier attitude.

4. "However, the high precision inertial measurement unit based on MEMS is usually composed of multiple devices, which still has large volume and high power consumption problems." – Pls provide suitable references here. The hybrid assembly of stand-alone accelerometers and gyroscopes to realize an IMU is error-prone for various reasons. Briefly comment on the same.

Introduction: Added the reference.

Bian, Y.; Hu, Y.; Li, B.; et al. Research status and development trend of MEMS inertial sensor. Metrology & Measurement Technology 2019, 39, 50–56.

The main problem of multi-device assembly is that it requires high assembly accuracy, otherwise, the cross-coupling coefficient between each axis will be large, which will affect the overall accuracy.

5. The manuscript will benefit from thorough proofreading. For example, Line 77 should be "G. H. Bryan" and Line 79, whether the Bryan effect or Brian effect. Pls, check.

Thoroughly checked and revised the manuscript.

6. Please comment on the rationale for choosing the IMU's geometrical dimensions listed in Table 1.

At present, due to factors such as application requirements, processing, and packaging, the plane dimensions of mems gyroscopes and accelerometers are generally within 1cm*1cm. The thickness of the device fabricated by the DDSOG process is generally 60 to 120 μm. Therefore, the overall size of the device is set to 9mm*9mm*0.1mm. Other dimensions are set based on the previous research, according to the performance requirements of the device and the frequency requirements of the control circuit.

7. Even though it is simulation work, authors are suggested to compare the metrics of the proposed IMU with reported accelerometers and gyroscopes. What are the sensitivity, resolution, and other parameters of the gyroscope? Authors have focussed only on the accelerometer's scale factor (i.e., sensitivity) with some temperature studies. Other quantitative metrics of the accelerometer are ignored in the present work—Pls comment.

Since the single-chip integrated gyroscope accelerometer proposed in this paper is an inertial device structure. For the resonant accelerometer, its sensitivity is represented by a scale factor (independent of the measurement and control circuit), and its resolution is affected by the structure and the measurement and control circuit, and will be further reported after the preparation is completed. For the ring gyroscope, its sensitivity is represented by a precession factor, generally 0.27; similarly, its resolution is affected by the structure and the measurement and control circuit.

The temperature analysis is performed because the material properties of the silicon material are easily affected by temperature, and the analysis needs to be focused during the design.

For resonant accelerometers, the general focus is on the resonant frequency, scale factor, and temperature sensitivity at the structural level. Other indicators, such as zero offset, zero offset stability, scale factor stability, scale factor repeatability, etc., need to be tested on the prototype.

8. Most of the references are not published in the recent past. The authors may consider updating the references with recent manuscripts on accelerometers and gyroscopes. Also, please ensure that all the references are relevant to the text against which they are mentioned.

Updated recent research literature closely related to this paper.

[1] Nazir, S.; Kwon, O.S.; et al. Micro-electromechanical systems-based sensors and their applications. Applied Science and Convergence Technology 2022, 31, 40–45.

[2] Jia, J.; Ding, X.; Qin, Z.; Ruan, Z.; Li, W.; Liu, X.; Li, H. Overview and analysis of MEMS Coriolis vibratory ring gyroscope. Measurement 2021, 182, 109704.

[3] Sobreviela-Falces, G.; Pandit, M.; Young, D.; Pili, C.; Mcintosh, J.; Abbott, J.; Brook, G.; Reed, M.; Steinmann, P.; MacCarthy, N.; et al. A Navigation-Grade Mems Vibrating Beam Accelerometer. In Proceedings of the 2022 IEEE 35th International Conference on Micro Electro Mechanical Systems Conference (MEMS). IEEE, 2022, pp. 782–785.

[4] Shkel, A.M.; Wang, Y., Inertial Sensors and Inertial Measurement Units. In Pedestrian Inertial Navigation with Self-Contained Aiding; 2021.

[5] Bian, Y.; Hu, Y.; Li, B.; et al. Research status and development trend of MEMS inertial sensor. Metrology & Measurement Technology 2019, 39, 50–56.

[6] Song, Z.; Cui, J.; Zhao, Q. A Silicon Resonant Accelerometer with Vibrating Beam Integrated with Comb Fingers Sensing Structure. In Proceedings of the 2019 IEEE 14th International Conference on Nano/Micro Engineered and Molecular Systems (NEMS). IEEE, 2019, pp. 477–481.

[7] Xiong, X.; Zheng, W.; Wang, K.; Li, Z.; Yang, W.; Zou, X. Sensitivity enhancement of Mems resonant accelerometers by using electrostatic spring. In Proceedings of the 2020 IEEE International Symposium on Inertial Sensors and Systems (INERTIAL). IEEE, 2020, pp. 1–3.

[8] Liu, M.; Cui, J.; Li, D.; Zhao, Q. A 3 PPM/ ◦ C temperature coefficient of scale factor for a silicon resonant accelerometer based on crystallographic orientation optimization. In Proceedings of the 2021 21st International Conference on Solid-State Sensors, Actuators and Microsystems (Transducers). IEEE, 2021, pp. 116–119.

Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

1. In Fig. 5, Please provide the zoom-in view of the accelerometer and the gyroscope from the whole structure (Figure 3 may be removed in that case). From this picture, explain the fabrication flow diagram across different cross-sections, say, A-A' and B-B.' The proposed flow diagram is primitive and made of text-book material.

2. Authors are suggested to tabulate the performance comparison of the current device (simulation results as applicable) with the hitherto reported fabricated devices (experimental results of others' work. You may include a footnote mentioning the same).

3. From the simulation results, can you comment on the cross-sensitivities of the resonant accelerometer?

 

Author Response

Since the response letter contained some images, we uploaded them as attachments.

Please see the attached PDF file. Thank You.

Author Response File: Author Response.pdf

Round 3

Reviewer 3 Report

Unfortunately, the authors are not willing to make changes and defend their stand. One possible reason could be that answering the queries needs more effort from the authors. Please note that the reviewers do spend their time only with the professional aim of improving the quality of the article. The manuscript must be clear (without any ambiguity) and useful to the research community.

1. Regarding fabrication flow diagram: I do not understand the difficulty in providing a detailed flow diagram across different cross-sections. From the given figure, it is difficult to identify different parts, i.e., DETF, proof mass, leverage mechanism, etc., of the accelerometer and where is the gyroscope? A google image search on the "Silicon-on-glass process" will give sufficient results to get a flow diagram, as shown in Fig. 4 of the manuscript. However, the authors should apply the SOG process to their devices and provide detailed flow diagrams with all the components that would benefit the readers. They need not give the mask details, but a conceptual flow diagram would be beneficial.

2. "the single-chip integration of the gyroscope and the accelerometer can be realized." - Please provide the fabrication feasibility of such an integrated device with neat cross-sectional diagrams.

3. It is obvious that geometrical dimensions would determine the terminal characteristics of any device. Therefore, please consider typical dimensions, evaluate the possible performance metrics from simulation results, and compare the same with the experimental results reported by other researchers. One possible approach is to use "Figure of Merit," which would cover different geometrical dimensions.

4. What is the meaning of the 'size' of the scale factor? Not clear to me. It requires rephrasing.

4. For our accelerometer, we could find some cross-talk even at the simulation level without considering fabrication errors. Nevertheless, if it is zero for your device, by all means, you can skip the same.

Author Response

Since the response letter contained some images, we uploaded them as attachments.

Please see the attached PDF file. Thank You.

Author Response File: Author Response.pdf